Pantograph antenna



Patente-d Jan. 7, 1941 UNITED STATES PATE-NT i oer-TCE j y2,227,929ArAN'rVOGRAPH ANTENNA De Witt Rugg Goddard, Riverhead, N. Y., assignerto Radio Corporation of America, a corporation of Delaware ApplicationJune 29, 1939, Serial No. 281,915

5 claims. (o1. 25o-11) This invention relates to a directional antennasystem which is particularly adapted to measure the vertical arrivalangle of short Wave radiations.

In the past the measurement of the vertical angle of arrival of radiosignals has been accomplished with considerable difjculty and hasnecessitated the use of complicated receiving equipment. In addition,the actual angle of arrival was obtained only after considerablecomputations had been, made. It is therefore an object of this inventionto provide a directive antenna system by means of which the verticalangle of arrival of radiated waves may be measured directly. Furtherobjects of this invention include the provision of an improveddirectional antenna system; the provision of a readily adjustabledirectional antenna; the provision of a directional antenna whichy isnot adversely affected by waves which are reflected from the surface ofthe earth; and the provision of a directional antenna system which maybe used to provide an inclined plane of zero signal which may be used toguide aircrafts to blind landings.

This invention will be better understood from the following description`when considered in connection with the accompanying drawing, in whichFigure 1 illustrates the electrical connections of an antenna systeminaccordance with this invention; Figure 2'is a plan view of a mechanicalarrangement suitable for adjusting the angle of reception of thedirective antenna system; and Figure 3 is a4 perspective Viewillustrating the general arrangement and connection .of the antennasused in the directive system herein proposed.

Referring to the drawing, the antenna system comprises four mutuallyparallel dipole antennas A, B, C and D which are supported at the fourcorners of a parallelogram, the sides of which are substantially a halfwave length long at the operating frequency, the diagonals of which lie,respectively, in vertical and horizontal planes.

Referring particularly to Figures 1 and 3, dipole antennas A and B areconnected by a transmission line L that contains one reversal, that is,the right hand portion of dipole A is connected to the left hand portionof dipole B, and vice versa. Dipoles C and D are connected in the samefashion, and dipoles C and B are likewise similarly connected. At anyconvenient point, adjacent dipole B, for example, a transmission line Tis connected between the antenna system and a receiver R. v

The arrangement shown produces a null or point of zero reception forsignals arriving at the angle a. line through antennas A and'B makes'tothe ground. The voltage at antenna B whichis' produced by a signal WhoseWave iront is proceed;4 ing in the direction of the arrows P parallel toa line drawn through antennas A and B is Zero, as will now beexplained.The voltageat antenna B is the resultant of the voltage picked up by allthe antennas. That produced by antenna A is in phase opposition to thatproduced' by'antennaB due to the reversal of the connection in transmissionline L. Likewise, the voltage produced by antenna C is in phaseopposition to the voltage produced by antenna. D due to the reversal of.1*'5 transmission line M. Consequently, there is noy voltage present atantennas B or D, and the transmission line N connecting the lattervantennas transfers no energy and the lreceiverflt receives no signals.

Consideration will now be given tothe effect of the energy which isreflected vfrom the ground and which impinges on the dipole antennas.The reflected energy will have the same angle to the ground as thedirectly received energy but :the Wave front will proceed in a directionindicated by the arrows O, since the angle of incidence is equal to theangle of reflection. The reflected energy travels in a direction whichis parallel to a line passing through antennas C and A, which is alsoparallel to a line passing through antenna B and D. The reflected energywill therefore induce a voltage in antenna C which will travel throughtransmission lines M, N and L and will arrive at antenna A at a timewhich is equal to three half wave lengths later. also suffer three phasereversals while traversing this path. Each half wave length oftransmission lineand each phase reversal', respectively, provide phaseshift, so that the total phase shift experienced by the induced voltagein the three sections is equal to 1080", or three complete revolutions.In other words, the voltage that appears at dipole antenna A due to thevoltage induced in antenna C is in phase with the voltage at antenna C.However, the voltage picked up by dipole A is in phase opposition tothat picked up by dipole C due to the half Wave spacing between C and A.Therefore, the voltage at A is bucked oui-l by the voltage induced inantenna C. This combination of voltages is, of course, true for anypoint on the transmission lines N, M or L, and is therefore true at thepoint at which transmission line T is connected to the system. Thereceiver R, therefore, receives no signal from voltages which areinduced in antennas A and C. An-

This voltage will,

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tennas B and D are likewise in line with the reected signal wave front,are likewise spaced a half wave length apart, and the induced voltagesare likevn'se in phase opposition so that no signal will be reproducedin the receiver due to voltages induced in antennas B and D. It isapparent, therefore, that the antenna arrangement illustrated is notIreceptive to signals arriving from the directions indicated by thearrows O and P. Signals arriving from directions other than 0 and P,however, are not completely balanced out since the eiective distancebetween the various dipole antennas is not equal to a half wave lengthat any other angle of approach.

In order to provide a directive antenna system which is readily adaptedto be used for the measurement of signals arriving at an unknown angle,an arrangement similar to that illustrated in Fig. 2 is proposed. Eachof the four dipole antennas is held at a xed distance from each adjacentantenna by any suitable insulating means the length of which ispreferably adjustable. For example, the transmission lines themselvesmay be rigid telescopic conductors. The lengths of the dipole antennasare also preferably adjustable to permit operation over a range offrequencies. The lower dipole C is held in fixed position, while theupper dipole A is arranged to be moved vertically in a rigid insulatedsupport S so that the angle of reception may be adjusted. Thearrangement is similar to a pantograph, the insulating spacers havingexible couplings at the respective antennas. By moving antenna A in avertical direction the angle of minimum reception is varied, and theactual angle may be determined by means of a Calibraw tion which isprovided along the vertical supporting member S. The angle of approachis therefore directly indicated, and computations are not necessary. InFigure 2, the antenna is illustrated in two positions. When extended;antennas A', B', and D produce a null at the receiver for a signal whicharrives at an angle U while in its lower position the antenna produces anull indication for signals arriving at an angle V.

While I have illustrated this antenna in connection with a receiver itis also adapted to be (used in connection with a transmitter. In such`an application it will provide a radiation pattern which has a plane ofzero signal which makes an angle with the ground. This angle is readilyadjustable as will be seen, and may be used to direct the flight of anaircraft, for example, to permit blind landings.

I claim:

1. A directional antenna system comprising four mutually parallelhorizontal dipole antennas having oppositely extending arms, saidantennas being positioned so as to define the corners of a parallelogramthe diagonals of which are, respectively, horizontal and vertical, andconducting means connected between said oppositely extending arms sothat currents induced in said conducting means by one of said antennasare in phase opposition to currents induced in said conducting means byanother of said antennas.

2. A directional antenna system comprising a plurality of mutuallyparallel dipole antennas 'having oppositely extending arms, means forsupporting said dipole antennas at the four corners of a parallelogramthe diagonals of which are, respectively, horizontal and vertical, apair of conductors for connecting alternate arms of said antennas inparallel so that currents induced in said conductors by one of saidantennas are in phase. opposition to currents simultaneously induced inan adjacent antenna, and means for varying the relative positions ofsaid dipole antennas to change the vertical angle of minimum response.

3. A directional antenna system comprising a plurality of mutuallyparallel dipole antennas, means for supporting said antennas at the fourcorners of a parallelogram, the sides of which are substantially a halfwave length long at the operating frequency, means connected betweenadjacent dipole antennas for connecting said dipole antennas inparallel, the polarity of said connecting means being reversed betweenadjacent antennas, and means for varying the position of one of saidantennas with respect to a diagonally positioned antenna to adjust saidsystem to indicate the horizontal angle of approach of radio wavesimpinging on said system.

4. A directional antenna system comprising a plurality of mutuallyparallel dipole antennas, means for supporting said antennas at the fourcorners of a parallelogram., the sides of which are substantially a halfwave length long at the operating frequency and the diagonals of whichlie respectively in vertical and horizontal planes, means connectedbetween adjacent dipole antennas for connecting said dipole antennas inparallel, the polarity of said connecting means being reversed betweenadjacent antennas, and means for varying the position of one of saidantennas with respect to a diagonally positioned antenna to adjust saidsystem to indicate the horizontal angle of approach of radio wavesimpinging on said system.

5. A device of the character described in claim 4 which includesindexing means associated with said one antenna for indicating thevertical angle of minimum reception of said system.

DE WITT RUGG GODDARD.

